Rate-responsive pacemaker with minute volume determination and EMI protection

Abstract

A rate responsive pacemaker includes a noise sensor for sensing noise on the leads. If noise is detected, the pacemaker switches to a mode wherein a metabolic demand parameter is ignored. The noise is preferably detected by using test signals which are also used to measure the metabolic demand parameter.

We claim: 
     
       1. A rate responsive pacemaker comprising: a sensor for sensing cardiac activity and generating a corresponding cardiac sense signal;   a pace generator for generating pacing signals in response to a first and a second command signal;   a metabolic demand sensor for sensing a metabolic demand parameter and generating a corresponding metabolic indicated signal;   a noise sensor for generating a noise signal when sensing noise; and   a controller receiving said sensor, metabolic indicated and noise signals and generating said first command responsive to said metabolic indicated signal in absence of noise and said second command independent of said metabolic indicated signal in the presence of noise.   
     
     
       2. The pacemaker of claim 1 wherein said controller includes a mode selector, said mode selector receiving said sensor signal and generating a first mode signal when said sensor signal indicates an intrinsic cardiac rate below a preset value and a second mode signal when said intrinsic cardiac rate is above said preset value. 
     
     
       3. The pacemaker of claim 1 wherein said metabolic demand parameter comprises a thoracic impedance. 
     
     
       4. The pacemaker of claim 1 wherein said controller further receives signals indicative of the lead impedance and wherein said controller generates said second command if said impedance exceeds a preset threshold. 
     
     
       5. The pacemaker of claim 4 wherein said controller generates a third command in response to a high impedance, said third command being sent to said metabolic demand sensor to disable the same. 
     
     
       6. A rate response pacemaker comprising: a lead extending to a cardiac chamber;   a sensor for sensing cardiac activity from said lead and generating a corresponding cardiac sense signal;   a pace generator for generating pacing signals in response to a first and a second command signal;   a metabolic demand sensor for sensing a metabolic demand parameter and generating a corresponding metabolic indicated signal;   a noise sensor for generating a noise signal when sensing noise on said lead; and   a controller receiving said sensor, metabolic indicated and noise signals and generating said first command responsive to said metabolic indicated signal in absence of noise and said second command independent of said metabolic indicated signal in the presence of noise.   
     
     
       7. The pacemaker of claim 6 wherein in the presence of noise said controller generates commands for pacing at a rate prior to noise detection. 
     
     
       8. The pacemaker of claim 6 further comprising a test generator for generating a test pulse and a response sensor for sensing a response on said lead to said test pulse. 
     
     
       9. The pacemaker of claim 8 wherein said response generator senses said response to determinate said metabolic demand parameter. 
     
     
       10. The pacemaker of claim 9 wherein said test pulse measures a transthoracic impedance. 
     
     
       11. The pacemaker of claim 8 wherein said test generator generates a first test pulse and a second test pulse and wherein said noise is detected by comparing responses from said lead to said first and second test pulses. 
     
     
       12. The pacemaker of claim 8 wherein said test generator generates multiphase test signals. 
     
     
       13. A pacemaker comprising: a sensor for sensing intrinsic activity in a patient's heart and generating in response sensed signals;   a pace generator for generating pacing pulses in response to commands;   a controller receiving said sensed signals and generating in response said commands; and   a noise sensor sensing external noise and in response altering the operation of said controller, said noise sensor including a test generator for generating two test pulses of equal magnitude and a test sensor for comparing the responses to said test pulses, said response being indicative of said external noise.   
     
     
       14. A pacemaker comprising: a sensor for sensing intrinsic activity in a patient's heart and generating in response sensed signals;   a pace generator for generating pacing pulses in response to commands;   a controller receiving said sensed signals and generating in response said commands; and   a noise sensor sensing external noise and in response altering the operation of said controller, said noise sensor including a test generator for generating a multiphase test pulse, said multiphase test pulse including at least two test portions of equal magnitude but different phases.